Transmission power allocation method, communication device and program

ABSTRACT

There is provided a method for allocating a transmission power to a second communication service making secondary usage of a spectrum assigned to a first communication service, in a node which is able to communicate with a secondary usage node, comprising the steps of: determining an interference power acceptable for two or more second communication services when the two or more second communication services are operated; distributing a transmission power depending on the interference power among the two or more second communication services according to a first rule; distributing the transmission power similarly according to a second rule; selecting one of the first rule and the second rule based on transmission powers distributed according to the first rule and transmission powers distributed according to the second rule; and allocating the transmission powers distributed according to the selected rule respectively to the two or more second communication services.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmission power allocation method,a communication device and a program.

2. Description of the Related Art

Discussions have been taking place recently regarding secondary usage ofa spectrum assigned for primary usage to provide a secondarycommunication service depending on the use condition of the spectrum.For example, the standard specification for allowing an unused channelcontained in a spectrum of the U.S. digital TV broadcast (TV whitespaces) to be available for radio communication has been studied in theIEEE802.22 working group (cf. “IEEE802.22 WG on WRANs”, [online],[Searched on Jan. 5, 2009], Internet <URL:http://www.ieee802.org/22/>).

Further, according to the report from FCC (Federal CommunicationsCommission) on November 2008, the discussions are directed towardpermitting secondary usage of TV white spaces by using a communicationdevice that fulfills a certain condition and has received anauthorization. The FCC's report accepts the above-described standardspecification of IEEE802.22 which is the pioneering work on thestandardization of secondary usage of TV white spaces and furthercoverts the moves of a new study group in IEEE. Technically, because itis required to perform signal detection at the level of −114[dBm] (SNRis about −19[dB] when NF (Noise Figure) is 11[dB], for example) with useof existing technology, for example, an auxiliary function such asgeo-location database access is expected to be necessary (cf. “SECONDREPORT AND ORDER AND MEMORANDUM OPINION AND ORDER”, [online], [Searchedon Jul. 10, 2009], Internet<URL:http://hraunfoss.fcc.gov/edocs_public/attachmatch/FCC-08-260A1.pdf>).Further, the FCC is searching for opening a 250 MHz band, which is apart of a 5 GHz band, as a new channel for secondary usage.

Furthermore, in the EU, there are moves afoot to universally allocate adedicated control channel called CPC (Cognitive Pilot Channel) formaking DSA (Dynamic Spectrum Access) under a long-term strategy.Allocation of CPC is incorporated in the agenda of ITU (InternationalTelecommunication Union)-WP11 in 2011. Technological studies for asecondary usage system that makes DSA are also being progressed in IEEESCC (Standards Coordinating Committee) 41.

In such a background, several research reports have been releasedrecently concerning secondary usage of a spectrum in the case ofassuming a broadcasting system, a satellite communication system, amobile communication system or the like as a primary system. Forexample, Alan Bok et al., “Cognitive Radio System using IEEE802.11a overUHF TVWS”, Motorola, October 2008 proposes a system architecture in thecase of operating a radio system with use of the IEEE802.22 standard onTV white spaces of UHF (Ultra High Frequency). Further, D. Gueny et al.,“Geo-location database technique for incumbent protection in the TVWhite space”, DySPAN, October 2008 also intends use of TV white spacesand proposes a form that utilizes positional information of a servicearea of a primary system as external information.

On the occasion of secondary usage of a spectrum, it is generallynecessary for a system on the part of secondary usage (secondary system)to carry out the operation that does not degrade the communicationquality of a primary system. Therefore, when transmitting a radio signalin the secondary system, it is desirable to control its transmissionpower so as to avoid interference on a node of the primary system.

Regarding such control of a transmission power, in the case of secondaryusage of TV white spaces as proposed by Alan Bok et al. or D. Gueny etal., it can be confirmed beforehand that a channel for secondary usageis not used at all, and it is thus possible to determine in many casesthat a transmission power at the maximum level can be used. On the otherhand, H. Fujii and H. Yoshino (NTT docomo), “Spectrum sharing byadaptive transmit power control for low priority system and itsachievable capacity”, CrownCom, May 2008 proposes a technique thatprotects a node of a high-priority system by adaptively controlling atransmission power in a low-priority system.

Further, Inage et al., “Spectrum Sharing Based on Capacity ConservationRatio of Primary User”, IEICE Technical Report SR2009, May 2009 proposesa technique that, when a system such as a mobile communication system inwhich the receiving environment of a terminal varies depending onlocation due to fading or the like is the primary system, adopts theratio of capacity (capacity conservation ratio) between before and aftersecondary usage in the primary system as a protection criterion andmakes transmission power control for satisfying the capacityconservation ratio.

SUMMARY OF THE INVENTION

In order to make full effective use of a limited spectrum, it is notsufficient to achieve secondary usage of the above-described whitespace, which is a spectrum in an area where a communication servicerelated to primary usage (which is referred to hereinafter as a firstcommunication service) is not provided. One reason is that secondaryusage of the white space is utilization of a spectrum that is apparentlyavailable in the long and medium terms in a particular region, and anactual opportunity of usage is limited to an area where there are only asmall number of users of the first communication service. Further, asfor secondary usage of the TV white space in the United States, forexample, it is predicted that part of the spectrum is auctioned and aspectrum left for secondary usage is small.

Given such a situation, one possible approach is to make secondary usageof a spectrum within a service area of the first communication serviceunder permission of a coordinator (e.g. a base station) of the firstcommunication service, for example. Another possible approach is to makesecondary usage of a spectrum that is unavailable for the firstcommunication service in an area inside or in the peripheral part of aservice area of the first communication service where signal receivingconditions are relatively unsuitable due to shadowing (shielding),fading or the like. In such cases of secondary usage, it is expectedthat a node of the primary system (which is referred to hereinafter as aprimary usage node) and a node of the secondary system (which isreferred to hereinafter as a secondary usage node) are located closer toeach other. Therefore, a mechanism of transmission power control thatsuppresses interference with enhanced adaptability is desirable. Forexample, because the technique taught by Inage et al. decreases theentire capacity of the primary system in one cell at a constant rate andallocates the amount of decrease to the secondary system, there remainsa possibility it becomes difficult to receive a radio signal (primarysignal) locally in one primary usage node due to interference of thesecondary usage node in the nearby vicinity.

In light of the foregoing, it is desirable to provide a novel andimproved transmission power allocation method, communication device andprogram that can reduce interference on the primary system to fallwithin an acceptable range while keeping the opportunity ofcommunication by secondary usage of a spectrum.

According to an embodiment of the present invention, there is provided amethod for allocating a transmission power to a second communicationservice making secondary usage of a spectrum assigned to a firstcommunication service, in a node able to communicate with a secondaryusage node that transmits a radio signal of the second communicationservice, including the steps of: determining an interference poweracceptable for two or more second communication services when the two ormore second communication services are operated; distributing atransmission power depending on the interference power among the two ormore second communication services according to a first rule;distributing a transmission power depending on the interference poweramong the two or more second communication services according to asecond rule; selecting one of the first rule and the second rule basedon transmission powers distributed according to the first rule andtransmission powers distributed according to the second rule; andallocating the transmission powers distributed according to the selectedrule respectively to the two or more second communication services.

In this configuration, when two or more second communication servicesare operated, an interference power acceptable for the secondcommunication services is determined, and then an appropriate rule isselected adaptively from the first and second rules for distributing atransmission power depending on the interference power. Then,transmission powers obtained by distributing the acceptable interferencepower according to the selected rule are respectively allocated to thetwo or more second communication services.

The first rule may be a rule for equally distributing the transmissionpower among the second communication services, and the second rule maybe a rule for distributing the transmission power among the secondcommunication services according to a distance between each secondaryusage node corresponding to each second communication service and a nodeinterfered by the second communication service.

The step of selecting one of the first rule and the second rule mayinclude comparing a total capacity calculated based on the transmissionpowers distributed according to the first rule with a total capacitycalculated based on the transmission powers distributed according to thesecond rule, and selecting a rule with a larger total capacity.

The total capacity may be calculated based only on transmission powerscorresponding to second communication services with a high priority, outof the transmission powers distributed according to the first rule orthe second rule.

The step of selecting one of the first rule and the second rule mayinclude comparing the number of links of second communication servicesthat can be established based on the transmission powers distributedaccording to the first rule with the number of links of secondcommunication services that can be established based on the transmissionpowers distributed according to the second rule, and selecting a rulewith a larger number of links.

The transmission power depending on the interference power may bedetermined based on quality of a radio signal required in the firstcommunication service, an interference level or a noise level in thefirst communication service, and a path loss on a communication pathabout each secondary usage node corresponding to each secondcommunication service.

According to another embodiment of the present invention, there isprovided a communication device including: a communication unit that isable to communicate with a secondary usage node that transmits a radiosignal of a second communication service making secondary usage of aspectrum assigned to a first communication service; and a control unitthat allocates a transmission power to each second communicationservice, wherein the control unit determines an interference poweracceptable for two or more second communication services when the two ormore second communication services are operated, distributes atransmission power depending on the interference power among the two ormore second communication services according to a first rule,distributes a transmission power depending on the interference poweramong the two or more second communication services according to asecond rule, selects one of the first rule and the second rule based ontransmission powers distributed according to the first rule andtransmission powers distributed according to the second rule, andallocates the transmission powers distributed according to the selectedrule respectively to the two or more second communication services.

According to another embodiment of the present invention, there isprovided a program causing a computer as a control unit, the computercontrolling a communication device including a communication unit thatis able to communicate with a secondary usage node that transmits aradio signal of a second communication service making secondary usage ofa spectrum assigned to a first communication service, wherein thecontrol unit allocates a transmission power to each second communicationservice and the control unit executes a process including: determiningan interference power acceptable for two or more second communicationservices when the two or more second communication services areoperated; distributing a transmission power depending on theinterference power among the two or more second communication servicesaccording to a first rule; distributing a transmission power dependingon the interference power among the two or more second communicationservices according to a second rule; selecting one of the first rule andthe second rule based on transmission powers distributed according tothe first rule and transmission powers distributed according to thesecond rule; and allocating the transmission powers distributedaccording to the selected rule respectively to the two or more secondcommunication services.

According to the embodiments of the present invention described above,it is possible to provide a transmission power allocation method, acommunication device and a program that can reduce interference on theprimary system to fall within an acceptable range while keeping theopportunity of communication by secondary usage of a spectrum.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram showing a first example in which a primary usagenode receives interference by secondary usage of a spectrum.

FIG. 1B is a diagram showing a second example in which a primary usagenode receives interference by secondary usage of a spectrum.

FIG. 2A is a first diagram to describe the effect of interferencedepending on a communication scheme and a channel direction.

FIG. 2B is a second diagram to describe the effect of interferencedepending on a communication scheme and a channel direction.

FIG. 2C is a third diagram to describe the effect of interferencedepending on a communication scheme and a channel direction.

FIG. 2D is a fourth diagram to describe the effect of interferencedepending on a communication scheme and a channel direction.

FIG. 3A is a first diagram to describe interference between secondcommunication services.

FIG. 3B is a second diagram to describe interference between secondcommunication services.

FIG. 4 is an explanatory view to describe an overview of a communicationsystem according to a first embodiment.

FIG. 5 is a block diagram showing an example of a logical configurationof a management node according to the first embodiment.

FIG. 6 is a flowchart showing an example of a flow of a transmissionpower determination process according to the first embodiment.

FIG. 7 is a flowchart showing an example of a flow of a transmissionpower distribution process according to the first embodiment.

FIG. 8 is a block diagram showing an example of a logical configurationof a terminal device according to the first embodiment.

FIG. 9 is a flowchart showing an example of a flow of a transmissionpower control process in a terminal device according to the firstembodiment.

FIG. 10 is an explanatory view to describe an overview of acommunication system according to a second embodiment.

FIG. 11 is a block diagram showing an example of a logical configurationof a management node according to the second embodiment.

FIG. 12 is a block diagram showing an example of a logical configurationof a terminal device according to the second embodiment.

FIG. 13 is a flowchart showing an example of a flow of a transmissionpower determination process according to the second embodiment.

FIG. 14 is an explanatory view to describe an application to TV band.

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

Hereinafter, preferred embodiments of the present invention will bedescribed in detail with reference to the appended drawings. Note that,in this specification and the appended drawings, structural elementsthat have substantially the same function and structure are denoted withthe same reference numerals, and repeated explanation of thesestructural elements is omitted.

Preferred embodiments of the present invention will be describedhereinafter in the following order.

1. Interference Control Model according to First Embodiment

-   -   1-1. Example of Interference by Secondary Usage of Spectrum    -   1-2. Description of Interference Control Model    -   1-3. Comparison of Channels for Secondary Usage    -   1-4. Study on Interference between Second Communication Services    -   1-5. Distribution of Transmission Powers among Second        Communication Services    -   1-6. Scope of Term “Secondary Usage”

2. First Embodiment

-   -   2-1. Overview of Communication System    -   2-2. Exemplary Configuration of Management Node    -   2-3. Exemplary Configuration of Terminal Device    -   2-4. Summary of First Embodiment    -   2-5. Alternative Example

3. Second Embodiment

-   -   3-1. Overview of Communication System    -   3-2. Exemplary Configuration of Management Node    -   3-3. Exemplary Configuration of Terminal Device    -   3-4. Summary of Second Embodiment

4. Application to TV Band

<1. Interference Control Model According to First Embodiment>

[1-1. Example of Interference by Secondary Usage of Spectrum]

Firstly, a case where a primary usage node receives interference due tosecondary usage of a spectrum is described briefly with reference toFIGS. 1A and 1B. FIGS. 1A and 1B are diagrams respectively showing anexample in which any primary usage node included in a primary systemreceives interference by secondary usage of a spectrum.

Referring to FIG. 1A, primary usage nodes Pn₁ and Pn₂ are located insidea cell 10 of a first communication service. The primary usage node Pn₁is a base station (PBS: Primary Base Station) that provides the firstcommunication service to a terminal device (which is also called UE:User Equipment) located inside the cell 10. The first communicationservice may be a given communication service including a digital TVbroadcasting service, a satellite communication service, a mobilecommunication service or the like. On the other hand, the primary usagenode Pn₂ is a terminal device (PUE: Primary User Equipment) that isprovided with the first communication service. The primary usage nodePn₁, the primary usage node Pn₂, and the other primary usage nodes inthe FIG. 1A transit and receive radio signals by using a spectrumassigned to the first communication service and thereby establishes aprimary system.

FIG. 1A also shows a plurality of secondary usage nodes Sn₁, Sn₂, Sn₃and Sn₄ located inside the cell 10. Those secondary usage nodes operatea second communication service by using a part or whole of the spectrumassigned to the first communication service (i.e. by making secondaryusage of the spectrum) in accordance with a predetermined spectrumpolicy and thereby establishes a secondary system. The secondcommunication service may be a radio communication service that isimplemented in conformity with an arbitrary radio communication protocolsuch as IEEE802.11a/b/g/n/s, Zigbee or WiMedia, for example. A pluralityof secondary systems may be established in a single cell, and, in theexample of FIG. 1A, different secondary systems are established in anarea 12 a, an area 12 b and an area 12 c inside the cell 10. Note that,although the primary usage node and the secondary usage node aredescribed separately for the sake of clarity of explanation, a part ofthe primary usage node may operate as the secondary usage node.

When the second communication service is operated inside the cell 10 ofthe first communication service as shown in FIG. 1A, there is apossibility that radio signals transmitted for the second communicationservice interfere with the first communication service. The example ofFIG. 1A shows the possibility that radio signals transmitted from thesecondary usage nodes Sn₁, Sn₂ and Sn₃ interfere with an uplink signaltransmitted from the primary usage node Pn₂ to the primary usage nodePn₁. In this case, there is a possibility that the primary usage nodePn₁ fails to normally receive the uplink signal, or, even if it receivesit, fails to obtain the desired service quality.

In FIG. 1B, just like FIG. 1A, the primary usage nodes Pn₁ and Pn₂ arelocated inside the cell 10 of the first communication service, and theprimary usage node Pn₁ serving as a base station provides the firstcommunication service to the primary usage node Pn₂ serving as aterminal device. Further, the secondary usage nodes Sn₁, Sn₂, Sn₃ andSn₄ are shown inside the cell 10 of the first communication service. Theexample of FIG. 1B shows the possibility that radio signals transmittedfrom the secondary usage nodes Sn₁, Sn₂, Sn₃ and Sn₄ interfere with adownlink signal transmitted from the primary usage node Pn₁ to theprimary usage node Pn₂. In this case, there is a possibility that theprimary usage node Pn₂ fails to normally receive the downlink signal,or, even if it receives it, fails to obtain the desired service quality.

One solution to prevent such interference by secondary usage of aspectrum and avoid an adverse effect such as degradation ofcommunication quality on the first communication service is to reduce atransmission power that is used for transmission of radio signals fromthe secondary usage nodes. On the other hand, reduction of atransmission power leads to a decrease in the capacity of the secondcommunication service and degradation of communication quality.Therefore, it is effective to increase a transmission power for thesecond communication service as much as possible within the range thatdoes not cause interference on the first communication service. Thus, arelationship between interference on the first communication service dueto secondary usage of a spectrum and a transmission power used in thesecondary usage nodes is described hereinbelow.

[1-2. Description of Interference Control Model]

Focusing attention on one-to-one relationship between the secondaryusage node on the part of giving interference due to secondary usage andthe primary usage node on the part of receiving interference (which isreferred to hereinafter as an interfered node), it is necessary tosatisfy the following relational expression (1) in order for theinterference to be accepted in the interfered node. Note that theinterfered node can correspond to the primary usage node Pn₁ in FIG. 1Aor the primary usage node Pn₂ in FIG. 1B, for example.

$\begin{matrix}{{SINR}_{required} \leq \frac{P_{{rx\_ primary},{primary}}}{P_{{rx\_ primary},{secondary}} + N_{primary}}} & {{Expression}\mspace{14mu}(1)}\end{matrix}$

In the above expression, SINR_(required) indicates the minimum SINR(Signal to Interference and Noise Ratio) that is required in theinterfered node. SINR_(required) may be the minimum receivingsensitivity of the interfered node, the minimum SINR given according toQoS (Quality of Service) or the like, for example. Further, P_(rx) _(—)_(primary,primary) indicates the reception level of a radio signal thatis required in the first communication service, and P_(rx) _(—)_(primary,secondary) indicates the reception level of a radio signalthat is transmitted from the secondary usage node in the interferednode. Further, N_(primary) indicates the interference or noise level(including one or both of the interference level and the noise level)that can be applied to the interfered node.

Further, the reception level of a radio signal is represented by thetransmission power of a radio signal and the path loss as shown in thefollowing relational expressions (2) and (3).P _(rx) _(—) _(primary,secondary) =P _(tx) _(—) _(secondary) /L _(path)_(—) _(tx) _(—) _(secondary)  Expression (2)P _(rx) _(—) _(primary,primary) =P _(tx) _(—) _(primary) /L _(path) _(—)_(tx) _(—) _(primary)  Expression (3)

In the above expression, P_(tx) _(—) _(secondary) indicates thetransmission power of a radio signal in the secondary usage node, andL_(path) _(—) _(tx) _(—) _(secondary) indicates the path loss on thecommunication path from the secondary usage node to the interfered node.Further, P_(tx) _(—) _(primary) indicates the transmission power of aradio signal in the first communication service, and L_(path) _(—) _(tx)_(—) _(primary) indicates the path loss on the communication path of aradio signal in the first communication service. Thus, the aboverelational expression (1) is deformed into the following expression.

$\begin{matrix}{{SINR}_{required} \leq \frac{P_{{rx\_ primary},{primary}}}{{P_{tx\_ secondary}/L_{{path\_ tx}{\_ secondary}}} + N_{primary}}} & {{Expression}\mspace{14mu}(4)}\end{matrix}$

Note that the interference or noise level N_(primary) included in theexpression (1) and the expression (4) can be calculated by the followingexpression, for example, with use of the Boltzmann constantk=1.38×10⁻²³[J/K], the absolute temperature T[K], the noise figure NFand the bandwidth BW[Hz].N _(primary) =I _(primary)+10^(10log) ¹⁰ ^((kT)+NF+10log) ¹⁰^((BW))  Expression (5)

In the above expression, I_(primary) may include inter-cell interferencein the first communication service, intra-cell interference in aheterogeneous environment where a femtocell, a small cell or a relaynode is overlaid by a macrocell, interference by out-of-band radiationor the like. Further, the path loss on the communication path of a radiosignal typically depends on the distance d between two nodes, and it canbe calculated by the following expression, for example.

$\begin{matrix}{{L_{path}(d)} = 10^{\frac{{- 10} - {\log_{10}{(\frac{\lambda}{4\pi\; d_{o}})}}^{2} + {10n\;{\log_{10}{(\frac{d}{d_{0}})}}}}{10}}} & {{Expression}\mspace{14mu}(6)}\end{matrix}$

In the above expression, d₀ indicates the reference distance, λindicates the wavelength of a carrier frequency, and n indicates thepropagation constant.

The relational expression (4) is further deformed into the followingexpression.

$\begin{matrix}{P_{tx\_ secondary} \leq {\left( {\frac{P_{{rx\_ primary},{primary}}}{{SINR}_{required}} - N_{primary}} \right) \cdot L_{{path\_ tx}{\_ secondary}}}} & {{Expression}\mspace{14mu}(7)}\end{matrix}$

If the transmission power of the secondary usage node is controlled soas to satisfy the relational expression (7), the interference can beaccepted in the interfered node at least concerning the one-to-onerelationship between the secondary usage node and the interfered node.Further, when a plurality of secondary usage nodes exist, it is neededto satisfy the following relational expression if the total number ofsecondary usage nodes acting as the source of interference is n.

$\begin{matrix}{{\sum\limits_{i = 1}^{n}\left( {P_{{tx\_ secondary},i}/L_{{{path\_ tx}{\_ secondary}},i}} \right)} \leq {\frac{P_{{rx\_ primary},{primary}}}{{SINR}_{required}} - N_{primary}}} & {{Expression}\mspace{14mu}(8)}\end{matrix}$

Consequently, on the assumption that the largest possible capacity orthe highest possible communication quality should be obtained in thesecond communication service as well, the interference power levelI_(acceptable) which is acceptable for the second communication serviceas a whole is given by the following expression.

$\begin{matrix}{{\sum\limits_{i = 1}^{n}\left( {P_{{tx\_ secondary},i}/L_{{{path\_ tx}{\_ secondary}},i}} \right)} = {\frac{P_{{rx\_ primary},{primary}}}{{SINR}_{required}} - {N_{primary}\left( {= I_{acceptable}} \right)}}} & {{Expression}\mspace{14mu}(9)}\end{matrix}$

Herein, since the parameters in the right-hand member of the expression(9) and the value of the path loss L_(path) _(—) _(tx) _(—)_(secondary,i) are known, only the transmission power P_(tx) _(—)_(secondary,i) depending on the interference power level I_(acceptable)becomes a parameter to be determined. It may be understood that theexpression (9) is an estimation formula to estimate the total sum ofacceptable interference powers on the primary system due to secondarysystems.

Specifically, as for a certain secondary usage node that makes secondaryusage of the spectrum assigned to the first communication service, it isdesirable to control transmission powers of secondary usage nodes insuch a way that the transmission powers satisfy the expression (9) as awhole.

[1-3. Comparison of Channels for Secondary Usage]

FIGS. 2A to 2D are diagrams to describe the effect of interference onthe occasion of secondary usage, depending on a communication scheme anda channel direction used in the first communication service.

FIGS. 2A to 2D show a primary usage node Pn₁ serving as a base stationand three primary usage nodes Pn₂, Pn₃ and Pn₄ serving as PUEs. Theprimary usage nodes Pn₁, Pn₂, Pn₃ and Pn₄ establish a primary system byusing OFDMA (Orthogonal Frequency Division Multiple Access) in theexamples of FIGS. 2A and 2B. The primary system in this case may beWiMAX (registered trademark) system, LTE (Long Term Evolution) system,LTE-A (LTE-Advanced) system or the like, for example. Further, theprimary usage nodes Pn₁, Pn₂, Pn₃ and Pn₄ establish a primary system byusing CDMA (Code Division Multiple Access) in the examples of FIGS. 2Cand 2D. The primary system in this case may be a UMTS (Universal MobileTelecommunications System), W-CDMA (Wideband-CDMA) or the like, forexample.

FIGS. 2A to 2D also show a secondary usage node Sn₁. The secondary usagenode Sn₁ transmits and receives a radio signal (secondary signal) forthe second communication service to and from another secondary usagenode located in an area 12 a, which can cause interference on theprimary usage nodes Pn₁, Pn₂, Pn₃ and Pn₄. The influential range of theinterference depends on a communication scheme and a channel directionof the first communication service which is the target of secondaryusage.

Referring first to FIG. 2A, when secondary usage is made on an uplinkchannel of the OFDMA system, interference can occur only on an uplinksignal from any one PUE to the base station in the primary system. Inthe example of FIG. 2A, the secondary signal from the secondary usagenode Sn₁ interferes with the uplink signal from the primary usage nodePn₂ to the primary usage node (base station) Pn₁. In this case, theuplink signals from the other PUEs are not affected by the secondarysignal because they are allocated in advance to different resourceblocks (or different frequency slots or time slots).

Referring next to FIG. 2B, when secondary usage is made on a downlinkchannel of the OFDMA system, interference can occur on downlink signalsfrom the base station to the respective PUEs in the primary system. Inthe example of FIG. 2B, the secondary signal from the secondary usagenode Sn₁ interferes with the downlink signals from the primary usagenode (base station) Pn₁ to the primary usage nodes Pn₂, Pn₃ and Pn₄.This is because the downlink signals (e.g. signals of a control channel)can be transmitted by using a common resource block or the like to theplurality of PUEs.

Referring then to FIG. 2C, when secondary usage is made on an uplinkchannel of the CDMA system, interference can occur on uplink signalsfrom the respective PUEs to the base station in the primary system. Inthe example of FIG. 2C, the secondary signal from the secondary usagenode Sn₁ interferes with the uplink signals from the primary usage nodesPn₂, Pn₃ and Pn₄ to the primary usage node (base station) Pn₁. Becausethe primary signals are typically spread to the entire band by usingspread codes assigned to the respective PUEs and transmittedsimultaneously in the CDMA system, the secondary signal can interferewith the primary signals from the plurality of PUEs.

Referring further to FIG. 2D, when secondary usage is made on a downlinkchannel of the CDMA system, interference can occur on downlink signalsfrom the base station to the respective PUEs in the primary system. Inthe example of FIG. 2D, the secondary signal from the secondary usagenode Sn₁ interferes with the downlink signals from the primary usagenode (base station) Pn₁ to the primary usage nodes Pn₂, Pn₃ and Pn₄.This is because the downlink signals (e.g. signals of a control channel)can be received in common by the plurality of PUEs and because theprimary signals are spread to the entire band and transmittedsimultaneously as in the uplink channel of the CDMA system.

The influential range of interference and the technical requirements inthe case of using the above-described four types of channels forsecondary usage are summarized in the following table 1.

TABLE 1 Table 1. Influential range of interference and technicalrequirements Communi- cation Channel direction scheme Uplink DownlinkOFDMA Interfered BS Interfered UEs node node Interfered a UE −> BSInterfered BS −> UEs link link Functional UL synchro- Functional DLsynchro- requirement nization requirement nization (Control channelidentifi- cation) Minimum −90 dBm Minimum −90 dBm receiving receivingsensitivity sensitivity CDMA Interfered BS Interfered UE node nodeInterfered UEs −> BS Interfered BS −> UEs link link Functional CodeFunctional Code requirement detection requirement detection Minimum −120dBm Minimum −120 dBm receiving receiving sensitivity sensitivity

Referring to the table 1, the influential range of interference is thesmallest in the uplink channel of the OFDMA system as described above.Specifically, interfere can occur only on the link from one UE (“a UE”)to the base station when making secondary usage of an uplink channel ofthe OFDMA system, whereas interfere can occur on the links related to aplurality of UEs when making secondary usage of another channel. Interms of functional requirements, detection of the spread code isnecessary for sensing of the primary signal in the CDMA system, whereasonly UL (uplink) or DL (downlink) synchronization is necessary in theOFDMA system, so that the CDMA system can be implemented more readily.Further, the minimum receiving sensitivity is −120 dBm (in the case ofUMTS) in the CDMA system, whereas it is −90 dBm (in the case of WiMAX)in the OFDMA system, for example, and it is less subject to interferencein the OFDMA system. Thus, on the occasion of secondary usage of aspectrum, it is desired to make secondary usage of the spectrum of theuplink channel, particularly, in the spectrum of the first communicationservice that employs the OFDMA scheme. In light of this, an embodimentwhich is described later in this specification is based on theassumption that secondary usage is made on the uplink channel of theOFDMA system. Note, however, that the present invention is applicable tothe downlink channel of the OFDMA system or channels using acommunication system other than the OFDMA system.

[1-4. Study on Interference Between Second Communication Services]

Interference which secondary usage of a spectrum causes on the firstcommunication service is described above. Hereinafter, interferencebetween second communication services in the case where there are aplurality of second communication services that make secondary usage ofthe spectrum assigned to the first communication service is described.

FIGS. 3A and 3B are diagrams to describe interference between secondcommunication services. FIG. 3A shows an example in which secondcommunication services are respectively operated in different adjacentcells. On the other hand, FIG. 3B shows an example in which two secondcommunication services are operated in the same cell.

FIG. 3A shows a primary usage node Pn_(1d) which is a base stationlocated inside a cell 10 d and a primary usage node Pn_(1e) which is abase station located inside a cell 10 e. Further, secondary usage nodesSn_(1d) and Sn_(2d) and a secondary usage node Sn_(2e) are includedinside the cell 10 d. Secondary usage nodes Sn_(1e) and Sn_(2e) and asecondary usage node Sn_(2d) are included inside the cell 10 e. Thesecondary usage nodes Sn_(1d) and Sn_(2d) operate the secondcommunication service inside an area 12 d. Further, the secondary usagenodes Sn_(1e) and Sn_(2e) operate the second communication serviceinside an area 12 e.

When the first communication service employs the OFDMA scheme, forexample, different frequencies are typically assigned as channelfrequencies used between adjacent cells by interference avoidancealgorithm between the adjacent cells. In the example of FIG. 3A, anuplink channel frequency of the cell 10 d is F1, and an uplink channelfrequency of the cell 10 e is F2. Therefore, when the uplink channel ofthe OFDMA scheme is the target of secondary usage, the frequency usedfor communication between the secondary usage nodes Sn_(1d) and Sn_(2d)is F1, and the frequency used for communication between the secondaryusage nodes Sn_(1e) and Sn_(2e) is F2. As a result, although the area 12d and the area 12 e overlap with each other in the example of FIG. 3A,the secondary signals transmitted and received by the secondary usagenodes Sn_(2d) and Sn_(2e) that are located in the overlapping part donot interfere (or collide) with each other.

On the other hand, FIG. 3B shows a primary usage node Pn_(1d) which is abase station located inside a cell 10 d. Further, secondary usage nodesSn_(1d) and Sn_(2d) and secondary usage nodes Sn_(1f) and Sn_(2f) areincluded inside the cell 10 d. The secondary usage nodes Sn_(1d) andSn_(2d) operate the second communication service inside an area 12 d.Further, the secondary usage nodes Sn_(1f) and Sn_(2f) operate thesecond communication service inside an area 12 f. In this case, thefrequency used for communication between the secondary usage nodesSn_(1d) and Sn_(2d) and the frequency used for communication between thesecondary usage nodes Sn_(1f) and Sn_(2f) are both F1. As a result, thesecondary signals transmitted and received by the secondary usage nodeSn_(2d) and the secondary usage node Sn_(2f) that are located in thepart where the area 12 d and the area 12 f overlap with each other arelikely to interfere with each other.

It is therefore understood that, when operating the second communicationservice by making secondary usage of the uplink channel of the OFDMAsystem, for example, in the spectrum assigned to the first communicationservice, it is desirable to give consideration to the existence ofanother second communication service at least in the same cell.

[1-5. Distribution of Transmission Powers Among Second CommunicationServices]

When the acceptable interference power of the second communicationservice is determined according to the above-described interferencecontrol model, if two or more second communication services exist in thesame cell, it is necessary to further distribute a transmission powerdepending on the acceptable interference power among those secondcommunication services. For example, in the case where a plurality ofsecondary usage nodes act as coordinators and start secondary usage of aspectrum, it is necessary to control their transmission powers so thatthe transmission powers of beacons that are transmitted from therespective coordinators satisfy the acceptable interference power as awhole. Further, the transmission power can be further distributed amongthe secondary usage nodes that subscribe to the second communicationservices. As a guideline for distributing the transmission power, threerules, i.e. equal type, unequal type and interfering margin reductiontype, are proposed.

(Equal Type)

The equal type is a distribution rule that equally allocatestransmission powers depending on the acceptable interference power thatis determined according to the above-described interference controlmodel to two or more second communication services. In the equal typedistribution rule, the value P_(tx) _(—) _(secondary,i) of thetransmission power which is allocated to the i-th (i=1, . . . , n)second communication service among n-number of second communicationservices is derived from the following expression.

$\begin{matrix}{{P_{{tx\_ secondary},i} = {{1/K} \cdot \left( {\frac{P_{{rx\_ primary},{primary}}}{{SINR}_{required}} - N_{primary}} \right)}},\mspace{20mu}{K = {\sum\limits_{i = 1}^{n}\frac{1}{L_{{{path\_ tx}{\_ secondary}},i}}}}} & {{Expression}\mspace{14mu}(10)}\end{matrix}$

The right side of the expression (10) is dividing the right side of theexpression (9) by the factor K on the basis of path loss L_(path) _(—)_(tx) _(—) _(secondary,i). Such a transmission power distribution ruleequally provides the opportunity of communication to the coordinators ofthe respective second communication services, and it is fair and clearas a service from the user's point of view. However, the interferencelevels on the primary usage node caused by the respective secondaryusage nodes are uneven. Note that, in the case of distributing thetransmission power among the secondary usage nodes that subscribe to thesecond communication service, the value of n used to determine thefactor K may be the total number of secondary usage nodes that subscribeto the second communication service instead of the total number ofsecond communication services.

(Unequal Type)

The unequal type is a distribution rule that unequally allocatestransmission powers depending on the acceptable interference power thatis determined according to the above-described interference controlmodel to two or more second communication services. In the unequal typedistribution rule, the value P_(tx) _(—) _(secondary,i) of thetransmission power depends on the distance between the secondary usagenode and the interfered node and is derived from the followingexpression.

$\begin{matrix}{P_{{tx\_ secondary},i} = {{1/n} \cdot \left( {\frac{P_{{rx\_ primary},{primary}}}{{SINR}_{required}} - N_{primary}} \right) \cdot L_{{{path\_ tx}{\_ secondary}},i}}} & {{Expression}\mspace{14mu}(11)}\end{matrix}$

The right side of the expression (11) is assigning weights at the ratioof the path loss for each secondary usage node relative to the total sumof the path losses to the value obtained by dividing the right side ofthe expression (9) by the total number n of second communicationservices. With such a transmission power distribution rule, thesecondary usage node that is more distant from the interfered node cangain larger opportunity of communication or communication distance. Theentire communication range can be thereby maximized.

(Interfering Margin Reduction Type)

The interfering margin reduction type is a distribution rule thatestimates the number of secondary usage nodes serving as the source ofinterference so as to include an extra number and thereby furtherreduces the possibility of causing interference on the primary usagenode (i.e. provides “interference margin”). In the interfering marginreduction type distribution rule, the value P_(tx) _(—) _(secondary,i)of the transmission power is derived from the following expression.

$\begin{matrix}{P_{{tx\_ secondary},i} = {\left( {\frac{P_{{rx\_ primary},{primary}}}{{SINR}_{required}} - N_{primary}} \right) \cdot {L_{{{path\_ tx}{\_ secondary}},i}/N_{estimation}}}} & {{Expression}\mspace{14mu}(12)}\end{matrix}$

In the expression (12), N_(estimation) indicates the estimated totalnumber of secondary usage nodes serving as the source of interferencewhich is estimated inclusive of an extra number. For example, the valueof N_(estimation) may be set so that the transmission power decreases by10[dB] if the total number of secondary usage nodes serving as thesource of interference is 10, and the transmission power decreases by20[dB] if it is 100.

The features of the three transmission power distribution rules aresummarized in the following table 2.

TABLE 2 Table 2. Features of transmission power distribution rules Equaltype Communication opportunity is equally provided to respectivecommunication services Fair and clear as service Interference levels onprimary usage node are uneven Unequal type Larger communicationopportunity or communication distance is obtained with distance frominterfered node Entire communication range can be maximized InterferingPossibility of causing interference is further margin reduced by settingof interference margin reduction type Transmission power can be setautonomously by secondary usage node (coordinate) Communicationopportunity or communication distance decreases with the estimated totalnumber of interference sources

It should be noted that a node that distributes a transmission power maydistribute the transmission power according to one rule that ispreviously selected among the above-described three transmission powerdistribution rules. Alternatively, a node that distributes atransmission power may distribute the transmission power by adaptivelyselecting the rule that consequently maximizes an evaluation value suchas the sum of capacities given to all secondary usage nodes (orsecondary usage nodes with a high priority) or the total number ofestablished secondary links.

[1-6. Scope of Term “Secondary Usage”]

In this specification, the term “secondary usage” typically meansutilization of an additional or alternative communication service (asecond communication service) using a part or whole of a spectrumassigned to a first communication service as described above. In thiscontext about the meaning of the term “secondary usage”, the firstcommunication service and the second communication service may beservices of different types or the same type. The services of differenttypes may be selected from services such as digital TV broadcastingservice, satellite communication service, mobile communication service,wireless LAN access service, P2P (Peer To Peer) connection service andthe like. On the other hand, services of the same type may contain, forexample, a relationship between a service of macro-cell provided by acommunication carrier and a service of femto-cell operated by users orMVNO (Mobile Virtual Network Operator). Additionally, services of thesame type may contain, for example, a relationship between a serviceprovided by a base station of a communication service according toWiMAX, LTE (Long Term Evolution), LTE-A (LTE-Advanced) or the like and aservice provided by relay station (relay node) to cover a spectrum hole.Further, a second communication service may be a service utilizing aplurality of fragmentary frequency bands aggregated using spectrumaggregation technology. Furthermore, a second communication service maybe a supplementary communication service provided by femto-cells, relaystations or small or medium sized base stations for smaller service areathan normal sized base stations within a service area of a normal sizedbase station. The subject matter of each embodiment described in thisspecification is applicable to every type of mode of such secondaryusages.

In the foregoing, the proposed interference control model is described,and the main points of the relevant technical concerns are describedsequentially. Based thereon, two embodiments of a transmission powercontrol method for improving the capability of transmission powercontrol on the occasion of secondary usage of a spectrum and suppressinginterference on the primary system are described hereinbelow.

<2. First Embodiment>

[2-1. Overview of Communication System]

FIG. 4 is an explanatory view to describe an overview of a communicationsystem according to a first embodiment of the present invention.

FIG. 4 shows a primary system 102 that operates a first communicationservice and secondary systems 202 a and 202 b that respectively operatesecond communication services. The primary system 102 includes amanagement node 100 and a plurality of primary usage nodes 104.

The management node 100 is a primary usage node that has a role tomanage secondary usage of the spectrum assigned to the firstcommunication service. Although the management node 100 is a basestation in the example of FIG. 4, the management node 100 is not limitedthereto. Specifically, the management node 100 may be a primary usagenode different from a base station, or it may be another node (e.g. adata server etc.) that is connected to a base station by wired orwireless means. In this embodiment, the management node 100 can gainaccess to a database 106 that stores location data indicating thelocations of primary usage nodes included in the primary system 102.

The primary usage node 104 is a node that transmits and receives radiosignals for the first communication service in the primary system 102.If the primary usage node 104 joins the primary system 102, locationdata indicating its location is registered into the database 106.

The database 106 is typically implemented as a geo-location database. Inthis embodiment, in response to a request from the management node 100,the database 106 outputs location data with respect to each primaryusage node to the management node 100. Note that the database 106 may beintegral with the management node 100 or it may be a separate unit fromthe management node 100.

On the other hand, the secondary system 202 a includes a terminal device200 a and a plurality of secondary usage nodes 204 a. Likewise, thesecondary system 202 b includes a terminal device 200 b and a pluralityof secondary usage nodes 204 b.

The terminal devices 200 a and 200 b are secondary usage nodes that havea role of a coordinator (SSC: secondary spectrum coordinator) thatoperates to start secondary usage of the spectrum assigned to the firstcommunication service. Specifically, the terminal devices 200 a and 200b determine the availability of secondary usage according to apredetermined spectrum policy, receive allocation of a transmissionpower from the management node 100, and start the second communicationservice with the secondary usage nodes 204 a or 204 b. The terminaldevices 200 a and 200 b may operate as an engine for cognitive radio(CE: Cognitive Engine), for example.

The secondary usage nodes 204 a and 204 b are nodes that respectivelytransmit and receive radio signals for the second communication servicein the secondary systems 202 a and 202 b, respectively.

In the following description, when there is no particular need todistinguish between the terminal devices 200 a and 200 b, they arereferred to collectively as the terminal device 200 by eliminating thealphabetical letter affixed to the reference numeral. The same appliesto the secondary systems 202 a and 202 b (the secondary system 202) andthe secondary usage nodes 204 a and 204 b (the secondary usage node204).

[2-2. Exemplary Configuration of Management Node]

(Description of Functional Blocks)

FIG. 5 is a block diagram showing an example of a logical configurationof the management node 100 shown in FIG. 4. Referring to FIG. 5, themanagement node 100 includes a communication unit 110, a databaseinput/output unit 120, a storage unit 130 and a control unit 140.

The communication unit 110 transmits and receives radio signals to andfrom the primary usage nodes 104 by using a communication interface thatcan include an antenna, an RF circuit, a baseband circuit or the like inaccordance with a given communication scheme of the first communicationservice. Further, the communication unit 110 receives location data ofthe terminal device 200 from the terminal device 200 and outputs thereceived location data to the control unit 140 as described in furtherdetail later.

The database input/output unit 120 mediates the access from the controlunit 140 to the database 106. Specifically, in response to a requestfrom the control unit 140, the database input/output unit 120 acquireslocation data indicating the location of the primary usage node 104 fromthe database 106, and outputs the acquired location data to the controlunit 140. Further, if the database input/output unit 120 receiveslocation data from the primary usage node 104 that newly joins theprimary system 102 through the communication unit 110, it registers thelocation data into the database 106. Further, the database input/outputunit 120 may acquire the location data stored in the database 106 inresponse to an inquiry from an external device and output the acquiredlocation data.

The storage unit 130 stores programs and data to be used for theoperation of each unit of the management node 100 by using a recordingmedium such as hard disk or semiconductor memory, for example. Further,in this embodiment, the storage unit 130 stores various parametersnecessary for calculation of the transmission power according to theabove-described interference control model. The parameters stored in thestorage unit 130 may include a parameter related to the quality of radiosignals required in the first communication service (e.g. a requiredradio signal reception level and a signal to interference and noiseratio) and a parameter related to the interference or noise level in thefirst communication service. Note that the values of those parametersmay be updated dynamically. For example, the value of the requiredquality of radio signals can be updated dynamically according to thetype of an application to be provided to the primary usage node.Further, for example, the value of the interference or noise level canbe updated dynamically by sensing through the communication unit 110.

The control unit 140 controls the overall functions of the managementnode 100 by using a control device such as a CPU (Central ProcessingUnit), for example. Further, in this embodiment, when the terminaldevice 200 makes secondary usage of the spectrum assigned to the firstcommunication service, the control unit 140 determines the acceptabletransmission power for the second communication service according to theabove-described interference control model. A transmission powerdetermination process that is performed by the control unit 140 isdescribed in further detail later. Further, when there are two or moresecond communication services, the control unit 140 distributes thedetermined transmission power to the two or more second communicationservices. A transmission power distribution process that is performed bythe control unit 140 is described in further detail later. The controlunit 140 then notifies the determined or distributed transmission powervalue to each terminal device 200 through the communication unit 110.

(Flow of Transmission Power Determination Process)

FIG. 6 is a flowchart showing an example of a flow of a transmissionpower determination process that determines the acceptable transmissionpower for the second communication service by the control unit 140 ofthe management node 100.

Referring to FIG. 6, the control unit 140 first receives location dataof the terminal device 200 from the terminal device 200 through thecommunication unit 110 (step S102). In this specification, the locationdata may include values of latitude and longitude measured by using theGPS functions or coordinate values with a point of origin at a givencontrol point measured by applying the direction of arrival estimationalgorithm or the like, for example. Further, the control unit 140 mayreceive not only location data of the terminal device 200 but alsolocation data of each secondary usage node 204 from the terminal device200.

Next, the control unit 140 acquires location data of the primary usagenode from the database 106 through the database input/output unit 120.Further, the control unit 140 acquires necessary parameters from thestorage unit 130 (step S104). Note that, in the case where secondaryusage is made on the uplink channel of the OFDMA system as in theexample shown in FIG. 2A, the interfered node is the base station only.In such a case, the control unit 140 acquires only the location data ofthe management node 100, which is the base station, as the location dataof the primary usage node. Further, the necessary parameters in the stepS104 correspond to the quality of radio signals required in the firstcommunication service, the interference or noise level in the firstcommunication service (or a parameter for calculating those levels) orthe like, for example.

Then, the control unit 140 determines the acceptable interference powerof the second communication service based on the location data and theparameters that are received in the step S102 and acquired in the stepS104, respectively (step S106). Specifically, the control unit 140 candetermine the acceptable interference power of the second communicationservice according to the expression (9) in the above-describedinterference control model, for example. For example, the quality ofradio signals required in the first communication service corresponds tothe term P_(rx) _(—) _(primary,primary)/SINR_(required) in theexpression (9). Further, the interference or noise level corresponds tothe term N_(Primary) in the expression (9). Further, the value of thepath loss L_(path) _(—) _(tx) _(—) _(secondary,i) in the expression (9)can be calculated according to the expression (6) by using the distanced that is derived from the location data of the primary usage node andthe location data of each terminal device 200. Note that the controlunit 140 may receive the value of each path loss L_(path) _(—) _(tx)_(—) _(secondary,i) from the respective terminal devices 200 in the stepS102 instead of calculating the value of each path loss L_(path) _(—)_(tx) _(—) _(secondary,i) from the location data, for example. The valueof the path loss L_(path) _(—) _(tx) _(—) _(secondary,i) can becalculated as a difference between the transmission power value of adownlink signal from the base station and the reception level of thedownlink signal in each terminal device 200.

Then, the control unit 140 determines whether it is necessary todistribute the value of the transmission power (step S108). For example,in the case where secondary usage is made by two or more terminaldevices 200 as illustrated in FIG. 4, the control unit 140 determinesthat it is necessary to distribute the value of the transmission poweramong the two or more terminal devices 200. In this case, the processproceeds to the step S110 and the control unit 140 performs atransmission power distribution process (step S110). On the other hand,in the case where there is only one terminal device 200 that makessecondary usage and it is not necessary to distribute the value of thetransmission power, the step S110 can be skipped.

After that, the control unit 140 notifies the value of the determined ordistributed transmission power to each terminal device 200 through thecommunication unit 110 (step S112). Note that the control unit 140 maynotify additional information such as a policy (e.g. a transmissionspectrum mask, a modulation method etc.) to be complied with by thesecondary usage node when making secondary usage of a spectrum, inaddition to the value of the transmission power, to each terminal device200. After that, the second communication service can be started betweenthe terminal device 200 and each secondary usage node 204.

(Flow of Transmission Power Distribution Process)

FIG. 7 is a flowchart showing an example of a flow of a transmissionpower distribution process by the control unit 140 of the managementnode 100 in the case where two or more terminal devices 200 exist,namely, where two or more second communication services are operated inthe same cell.

Referring to FIG. 7, the control unit 140 first distributes thetransmission power depending on the acceptable interference power thatis determined in the step S106 of FIG. 6 according to the first rule(step S202). Next, the control unit 140 distributes the transmissionpower depending on the acceptable interference power same as in the stepS202 according to the second rule (step S204). The first rule and thesecond rule may be the above-described equal type transmission powerdistribution rule and the unequal type transmission power distributionrule, respectively, for example.

Then, the control unit 140 evaluates the transmission power distributedaccording to the first rule and the transmission power distributedaccording to the second rule by predetermined evaluation criteria (stepS206). The predetermined evaluation criteria may be the total capacitythat is provided to all terminal devices 200 in the end, for example. Inthis case, the total capacity C can be evaluated according to thefollowing expression.

$\begin{matrix}{C = {{\sum\limits_{i = 1}^{n}C_{i}} = {\sum\limits_{i = 1}^{n}\left( {\log_{2}\left( {1 + \frac{P_{{tx\_ secondary},i}}{N_{i}}} \right)} \right)}}} & {{Expression}\mspace{14mu}(13)}\end{matrix}$

In the above expression, P_(tx) _(—) _(secondary,i) indicates thetransmission power distributed to the i-th terminal device 200, andN_(i) indicates the noise level of the i-th terminal device 200.

Further, in the expression (13), the control unit 140 may count only theterminal devices 200 with a high priority, out of the n-number ofterminal devices 200, for calculating the total capacity. The prioritycan be assigned depending on the type, contents or the like of thesecond communication service, for example. For example, a high prioritycan be assigned to the service for which small delay is needed, such asmotion picture delivery or network game, for example. Further, a highpriority can be assigned to the service to which high service charge isset so as to ensure a certain service quality. Then, the priority can bereceived together with the location data of the terminal device 200 inthe step S102 of FIG. 6, for example.

Further, the control unit 140 may evaluate the total number of links ofthe second communication services that can be established by using thedistributed transmission powers in the step S206 instead of evaluatingthe capacity as in the expression (13). In this case, the control unit140 first determines whether each pair of secondary usage nodes whichdesire for communication can establish communication according to thetransmission powers distributed to the respective terminal devices 200.Then, the number of links determined that communication can beestablished is counted as the total number of links of the secondcommunication services.

Then, the control unit 140 determines which of the first rule and thesecond rule is more appropriate by comparing the capacity or the totalnumber of links evaluated in the step S206 (step S208). For example,when the transmission powers distributed according to the first rule canachieve the larger capacity than the transmission powers distributedaccording to the second rule, the control unit 140 can determine thatthe first rule is more appropriate. Further, when the transmissionpowers distributed according to the second rule can achieve the largercapacity than the transmission powers distributed according to the firstrule, the control unit 140 can determine that the second rule is moreappropriate. When it is determined that the first rule is moreappropriate, the process proceeds to the step S210. On the other hand,when it is determined that the second rule is more appropriate, theprocess proceeds to the step S212.

In the step S210, the transmission powers distributed according to thefirst rule that is determined to be more appropriate are allocated tothe respective terminal devices 200 (step S210). On the other hand, inthe step S212, the transmission powers distributed according to thesecond rule that is determined to be more appropriate are allocated tothe respective terminal devices 200 (step S212). After that, thetransmission power distribution process shown in FIG. 7 ends.

Note that the case where the first rule and the second rule that canrespectively correspond to the equal type and the unequal type areevaluated in terms of the capacity or the number of links that can beestablished is particularly described above. However, it is not limitedthereto, and the transmission power distribution rules other than theequal type and the unequal type may be adopted. Further, three or moretransmission power distribution rules may be evaluated.

[2-3. Exemplary Configuration of Terminal Device]

(Description of Functional Blocks)

FIG. 8 is a block diagram showing an example of a logical configurationof the terminal device 200 shown in FIG. 4. Referring to FIG. 8, theterminal device 200 includes a first communication unit 210, a secondcommunication unit 220, a storage unit 230 and a control unit 240. Inthis embodiment, the terminal device 200 can communicate with themanagement node 100 through the first communication unit 210 and alsotransmit and receive radio signals for the second communication servicethrough the second communication unit 220.

The first communication unit 210 communicates with the management node100 in accordance with a given communication scheme. A channel used forcommunication between the first communication unit 210 and themanagement node 100 may be a cognitive pilot channel (CPC), which is acontrol channel, for example. The CPC may include an inbound CPC inwhich CPC information is extrapolated in an existing communicationsystem (e.g. the primary system 102) or an outbound CPC which is adedicated channel in which CPC information is interpolated, for example.

For example, the first communication unit 210 transmits location dataindicating the location of its own device to the management node 100 inresponse to an instruction (an instruction operation by a user or arequest from another node) for start of secondary usage of a spectrum orthe like. After that, the first communication unit 210 receives thevalue of the acceptable transmission power which is determined accordingto the above-described technique from the management node 100 andoutputs it to the control unit 240.

The second communication unit 220 transmits and receives radio signalsto and from the secondary usage node 204 in accordance with a givencommunication scheme. For example, when the terminal device 200 operatesas the coordinator of the second communication service, the secondcommunication unit 220 first performs sensing of radio signals of thefirst communication service and achieves synchronization of the uplinkchannel. Then, the second communication unit 220 transmits a beacon tothe secondary usage nodes 204 in the nearby vicinity on a regular basisby using the synchronized uplink channel. The transmission power used bythe second communication unit 220 is limited to the range that does notcause substantial interference on the primary usage node under controlof the control unit 240.

Note that, when the communication link between the first communicationunit 210 and the management node 100 is a radio link, the firstcommunication unit 210 and the second communication unit 220 may sharethe physically identical communication interface that can include anantenna, an RF circuit, a baseband circuit or the like. Thecommunication link between the first communication unit 210 and themanagement node 100 is called a backhaul link in some cases.

The storage unit 230 stores programs and data to be used for theoperation of each unit of the terminal device 200 by using a recordingmedium such as hard disk or semiconductor memory, for example. Further,in this embodiment, the storage unit 230 stores various parameters foroperation of the second communication service and control of thetransmission power. The parameters stored in the storage unit 230 mayinclude the location data of its own device (and other secondary usagenodes that subscribe to the second communication service according toneed), the acceptable transmission power notified from the managementnode 100, a spectrum mask, a modulation method or the like, for example.

The control unit 240 controls the overall functions of the terminaldevice 200 by using a control device such as a CPU, for example. Forexample, in this embodiment, the terminal device 240 controls the valueof the transmission power used for transmission of radio signals by thesecond communication unit 220 within the range of the acceptabletransmission power notified from the management node 100.

(Flow of Transmission Power Control Process)

FIG. 9 is a flowchart showing an example of a flow of a transmissionpower control process by the terminal device 200.

Referring to FIG. 9, upon detection of an instruction for start ofsecondary usage, for example, the first communication unit 210 transmitsthe location data of the terminal device 200 to the management node 100(step S302). In this step, not only the location data of the terminaldevice 200 but also the location data of other secondary usage nodes 204may be transmitted to the management node 100.

Next, the first communication unit 210 receives the value of theacceptable transmission power which is determined according to theabove-described interference control model from the management node 100(step S304). In this step, additional information such as a transmissionspectrum mask or a modulation method can be received in addition to theacceptable transmission power, for example.

Then, the control unit 240 starts the second communication service bycontrolling the transmission power used by the second communication unit220 so as to be within the range of the acceptable transmission powerthat is received in the step 304 (step S306). Note that, when startingthe second communication service, the control unit 240 may make a beacontransmitted from the terminal device 200 to the nearby secondary usagenodes include the value of the acceptable transmission power allocatedto the second communication service. The other secondary usage nodesthat subscribe to the second communication service can thereby alsoadjust their transmission powers so as not to cause substantialinterference on the primary usage node.

[2-4. Summary of First Embodiment]

The first embodiment of the present invention is described above withreference to FIGS. 4 to 9. In this embodiment, transmission powersallocated to the second communication service that makes secondary usageof the spectrum assigned to the first communication service isdetermined by the management node 100, which is the primary usage nodethat can access to the database 106, depending on the acceptableinterference power determined according to the above-describedinterference control model. Then, the determined transmission powers arenotified from the management node 100 to terminal devices 200, which arethe secondary usage nodes acting as the coordinator of the secondcommunication services. The terminal devices 200 can thereby makeadaptive control of the transmission power to be used for a secondcommunication service so that interference on the primary system 102 iswithin the acceptable level.

Further, according to the above-described interference control model, atransmission power is determined so that interference on the interferednode is within the acceptable level based on the quality of radiosignals required in the first communication service, the interference ornoise level in the first communication service, and the path loss on thecommunication path about one or more secondary usage nodes. It isthereby possible to eliminate (or at least reduce) the possibility thatit becomes difficult to receive a primary signal locally in a certainprimary usage node.

Further, the path loss on the communication path mentioned above can becalculated dynamically based on the location of the primary usage nodeand the location of the secondary usage node. Therefore, even when thelocation of the terminal device 200 changes, it is possible to determinethe transmission power in an adaptive manner so that interference on theinterfered node is within the acceptable level.

Further, according to the embodiment, in the case where two or moresecond communication services are operated, the transmission powerdepending on the acceptable interference power determined according tothe above-described interference control model is distributed among therespective second communication services according to the moreappropriate rule between the first rule and the second rule. The firstrule and the second rule may be the equal type distribution rule and theunequal type distribution rule described above, for example. The equaltype distribution rule can distribute the opportunity of communication(the capacity, the number of communication links etc.) in a fair andclear manner from the user's point of view. Further, the unequal typedistribution rule can distribute the transmission power so as tomaximize the communication range as a whole because a highertransmission power is allocated to the secondary usage node that is moredistant from the interfered node.

Furthermore, the more appropriate rule between the first rule and thesecond rule may be the rule with which the total capacity that isachieved in the end by using the allocated transmission powers islarger, for example. In this case, it is possible to maximize thecapacity that is effectively utilized by secondary usage of a spectrum.

Further, the more appropriate rule between the first rule and the secondrule may be the rule with which the total capacity related to the secondcommunication services with a high priority is larger in the capacitythat is achieved in the end by using the allocated transmission powers,for example. In this case, it is possible to selectively increase thecapacity by secondary usage of a spectrum so as to particularly satisfythe requirements of each application, the QoS requirements agreed by auser or the like.

Further, the more appropriate rule between the first rule and the secondrule may be the rule with which the number of links that can beestablished in the end by using the allocated transmission powers islarger, for example. In this case, it is possible to maximize the numberof users who can gain the opportunity of communication by secondaryusage of a spectrum.

Note that, in this embodiment, the case where the transmission powerused in the second communication service is controlled at the start ofthe second communication service is described. However, the processesshown in FIGS. 6, 7, and 9 may be executed after the start of the secondcommunication service, e.g. when the secondary usage node is moved orwhen the number of secondary usage nodes is changed, for example.

Further, the case where secondary usage is made on the uplink channel ofthe first communication service, i.e. when only the base station of thefirst communication service is taken into consideration as an interferednode is described in this embodiment. However, the present invention isapplicable to the case where a plurality of interfered nodes exist as amatter of course.

[2-5. Alternative Example]

In the above-described interference control model, the acceptabletransmission power for the second communication service is determined sothat interference on the interfered node among the primary usage nodesis suppressed within the acceptable level. On the other hand, thetransmission power used for the second communication service may bedetermined in consideration of the communication quality in thesecondary usage node also.

When one secondary usage node is regarded as an interfered node, it isnecessary to satisfy the following relational expression (14) in orderthat the interference is accepted.

$\begin{matrix}{{SINR}_{{i\_ required}{\_ secondary}} \leq \frac{P_{{{i\_ rx}{\_ secondary}},{{j\_ tx}{\_ secondary}}}}{\left( {I_{i,{primary}} + I_{i,{{k{({{k \neq i},{k \neq j}})}}{\_ tx}{\_ secondary}}}} \right) + N_{i}}} & {{Expression}\mspace{14mu}(14)}\end{matrix}$

In the above expression, SINR_(i) _(—) _(required) _(—) _(secondary)indicates the minimum SINR that is required in the i-th secondary usagenode, which is the interfered node. SINR_(i) _(—) _(required) _(—)_(secondary) may be the minimum receiving sensitivity of the interferednode, the minimum SINR given according to QoS or the like, for example.Further, P_(i) _(—) _(rx) _(—) _(secondary,j) _(—) _(tx) _(—)_(secondary) indicates the reception level that is required for a radiosignal (secondary signal) of the second communication service which istransmitted from the j-th secondary usage node to the i-th secondaryusage node. Further, I_(i,primary) indicates the interefence level byradio signals of the first communication service,I_(i,k(k≠i,k≠j)) _(—)_(tx) _(—) _(secondary) indicates the interference level by secondarysignals from other secondary usage nodes which are not the i-th or i-thsecondary usage node (i.e. which are not relevant to a desiredcommunication link). Further, N_(i) indicates the noise level applicableto the i-th secondary usage node. Note that the interference levelI_(i,k(k≠i,k≠j)) _(—) _(tx) _(—) _(secondary) by secondary signals fromother secondary usage nodes can be calculated by subtracting the totalsum of the path losses regarding the secondary usage nodes from thetotal sum of the transmission powers of the secondary usage nodes whichare not relevant to a desired communication link.

Therefore, the management node 100 according to the above-describedfirst embodiment may distribute the transmission power in such a waythat the transmission power allocated to each terminal device 200satisfies the above expression (14) in the transmission powerdetermination process in the step S110 shown in FIG. 6, for example.

<3. Second Embodiment>

In the first embodiment of the present invention, transmission powersallocated to the second communication service is determined by theprimary usage node (management node) which is accessible to the databasethat stores the location data of the primary usage node. This is apassive technique from the viewpoint of the terminal device (UE) thatmakes secondary usage. On the other hand, the terminal device that makessecondary usage may acquire necessary parameters and determine theacceptable transmission power for the second communication service in anactive manner. In this section, a case where the terminal device thatmakes secondary usage actively determines the acceptable transmissionpower is described as a second embodiment of the present invention.

[3-1. Overview of Communication System]

FIG. 10 is an explanatory view to describe an overview of acommunication system according to the second embodiment of the presentinvention.

FIG. 10 shows a primary system 302 that operates a first communicationservice and secondary systems 402 a and 402 b that respectively operatesecond communication services. The primary system 302 includes amanagement node 300 and a plurality of primary usage nodes 104.

The management node 300 is a primary usage node that has a role tomanage secondary usage of the spectrum assigned to the firstcommunication service. Although the management node 300 is a basestation in the example of FIG. 10, the management node 300 is notlimited thereto. In this embodiment, the management node 300 can gainaccess to a database 106 that stores location data indicating thelocations of primary usage nodes that are included in the primary system302.

On the other hand, the secondary system 402 a includes a terminal device400 a and a plurality of secondary usage nodes 204 a. Likewise, thesecondary system 402 b includes a terminal device 400 b and a pluralityof secondary usage nodes 204 b.

The terminal devices 400 (400 a and 400 b) are secondary usage nodesthat have a role of a coordinator (SSC) that operates to start secondaryusage of the spectrum assigned to the first communication service.Specifically, the terminal devices 400 determine the availability ofsecondary usage according to a predetermined spectrum policy, determinesthe acceptable transmission power by acquiring necessary parameters fromthe management node 300, and then starts the second communicationservices with the secondary usage nodes 204. The terminal devices 400may operate as an engine for cognitive radio (CE), for example.

[3-2. Exemplary Configuration of Management Node]

FIG. 11 is a block diagram showing an example of a logical configurationof the management node 300 shown in FIG. 10. Referring to FIG. 11, themanagement node 300 includes a communication unit 310, a databaseinput/output unit 120, a storage unit 130 and a control unit 340.

The communication unit 310 transmits and receives radio signals to andfrom the primary usage nodes 104 by using a communication interface thatcan include an antenna, an RF circuit, a baseband circuit or the like inaccordance with a given communication scheme of the first communicationservice. Further, the communication unit 310 transmits the location dataof the primary usage nodes 104 stored in the database 106 and parametersto be used for determination of a transmission power stored in thedatabase 106 or the storage unit 130 to the terminal device 400.

The control unit 340 controls the overall functions of the managementnode 300 by using a control device such as a CPU, for example. Further,in this embodiment, the control unit 340 transmits the above-describedlocation data and parameters to be used when the terminal device 400determines the acceptable transmission power according to theabove-described interference control model to the terminal device 400through the communication unit 310 (or another backhaul link). Thelocation data and parameters may be transmitted on a regular basis byusing a predetermined channel such as CPC, for example. Alternatively,the location data and parameters may be transmitted in response to atransmission request from the terminal device 400, for example.

[3-3. Exemplary Configuration of Terminal Device]

(Description of Functional Blocks)

FIG. 12 is a block diagram showing an example of a logical configurationof the terminal device 400 shown in FIG. 10. Referring to FIG. 12, theterminal device 400 includes a first communication unit 410, a secondcommunication unit 220, a storage unit 430 and a control unit 440.

The first communication unit 410 receives radio signals containing thedata and parameters transmitted from the management node 300 inaccordance with a given communication scheme. A channel used forcommunication between the first communication unit 410 and themanagement node 300 may be the above-described CPC, which is a controlchannel, for example.

Specifically, the first communication unit 410 attempts to receive thedata and parameters to be used for determination of a transmission powerfrom the management node 300 in response to an instruction for start ofsecondary usage of a spectrum or the like, for example. The data andparameters to be used for determination of a transmission power includethe location data of an interfered node, the quality of radio signalsrequired in the first communication service, the interference or noiselevel in the first communication service or the like, for example.Further, the data to be used for determination of a transmission powermay include location data indicating the locations of other secondaryusage nodes. If the first communication unit 410 receives the data andparameters from the management node 300, it outputs the received dataand parameters to the control unit 440. If, on the other hand, the firstcommunication unit 410 fails to receive the necessary data andparameters for some reasons such as unsuitable signal receptionenvironment, it provides notification to the control unit 440.

The storage unit 430 stores programs and data to be used for theoperation of each unit of the terminal device 400 by using a recordingmedium such as hard disk or semiconductor memory, for example. Further,in this embodiment, the storage unit 430 stores various parameters fordetermination of a transmission power for the second communicationservice and control of the transmission power. The parameters stored inthe storage unit 430 may include the location data of its own device(and other secondary usage nodes that subscribe to the secondcommunication service according to need), the parameters received fromthe management node 300 through the first communication unit 410 or thelike, for example.

The control unit 440 controls the overall functions of the terminaldevice 400 by using a control device such as a CPU, for example. Forexample, in this embodiment, when making secondary usage of the spectrumassigned to the first communication service, the control unit 440determines the acceptable transmission power for the secondcommunication service depending on the determined acceptableinterference power according to the above-described interference controlmodel. If the control unit 440 fails to receive radio signals from themanagement node 300 and is thus unable to acquire the latest locationdata of the primary usage node and necessary parameters, it determinesthe acceptable transmission power by counting in the margin for reducingthe possibility that causes interference on the primary usage node. Thetransmission power determination process is described in detail later.Then, the control unit 440 controls the value of the transmission powerto be used for transmission of radio signals by the second communicationunit 220 to fall within the range of the determined acceptabletransmission power.

(Flow of Transmission Power Determination Process)

FIG. 13 is a flowchart showing an example of a flow of a transmissionpower determination process for the control unit 440 to determine theacceptable transmission power for the second communication service.

Referring to FIG. 13, the control unit 440 first determines whetherradio signals are receivable from the management node 300 through thefirst communication unit 410 (step S402). If radio signals from themanagement node 300 are receivable, the process proceeds to the stepS404. If, on the other hand, radio signals from the management node 300are not receivable, the process proceeds to the step S408.

In the step S404, the control unit 440 acquires the location data of theprimary usage node serving as an interfered node that is received fromthe management node 300 through the first communication unit 410.Further, the control unit 440 acquires the parameters received frommanagement node 300 in the same manner (step S404). Note that, in thecase where secondary usage is made on the uplink channel of the OFDMAsystem as in the example shown in FIG. 2A, the interfered node is thebase station only. In such a case, the control unit 440 acquires onlythe location data of the management node 300, which is the base station,as the location data of the primary usage node. Further, the necessaryparameters in the step S404 correspond to the quality of radio signalsrequired in the first communication service, the interference or noiselevel in the first communication service (or a parameter for calculatingthose levels) or the like, for example.

Then, the control unit 440 determines the transmission power dependingon the acceptable interference power of the second communication servicebased on the location data and parameters received in the step S404(step S406). Specifically, the control unit 440 can determine thetransmission power depending on the acceptable interference power of thesecond communication service according to the expression (9) in theabove-described interference control model, for example. For example,the quality of radio signals required in the first communication servicecorresponds to the term P_(rx) _(—) _(primary,primary)/SINR_(required)in the expression (9). Further, the interference or noise levelcorresponds to the term N_(Primary) in the expression (9). Further, thevalue of the path loss L_(path) _(—) _(tx) _(—) _(secondary,i) in theexpression (9) can be calculated according to the expression (6) byusing the distance d that is derived from the location data of theprimary usage node and the location data of the terminal device 400.Note that the control unit 440 may calculate the value of the path lossL_(path) _(—) _(tx) _(—) _(secondary,i) as a difference between thetransmission power value of a downlink signal from the base station andthe reception level of the downlink signal instead of calculating itfrom the location data. Further, when another second communicationservice exists, the control unit 440 may distribute the transmissionpower according to the expression (10) of the equal type or theexpression (11) of the unequal type.

On the other hand, if radio signals from the management node 300 are notreceivable, in the step S408, the control unit 440 acquires the locationdata and parameters for determining a transmission power from thestorage unit 430 (step S408). For example, the control unit 440 mayreceive the location data of the interfered node and necessaryparameters through the first communication unit 410 when communicationwith the management node 300 becomes available and store them into thestorage unit 430 for later use. Further, when the types of the firstcommunication service which is the target of secondary usage are limitedto several candidates in advance, for example, a parameter indicatingthe quality of radio signals required in the first communication servicemay be stored as a default value in the storage unit 430.

Then, the control unit 440 determines the transmission power dependingon the acceptable interference power of the second communication servicebased on the location data and parameters acquired in the step S408(step S410). In this case, however, there is a possibility that theparameters used for determination of the transmission power are not thelatest. Thus, the control unit 440 adds a given margin to the value ofthe transmission power so as to reduce the possibility that causesinterference on the primary usage node. Specifically, the control unit440 can determine the transmission power according to the expression(12) of the interfering margin reduction type described above, forexample. The value of N_(estimation) in the expression (12) isdetermined to be inclusive of an extra number according to the number ofsecondary usage nodes 204 that possibly subscribe to the secondcommunication service, for example.

After that, the transmission power determination process by the controlunit 440 ends. Then, the second communication service is started betweenthe terminal device 400 and the respective secondary usage nodes 204 byusing the power level within the range of the determined acceptableinterference power.

[3-4. Summary of Second Embodiment]

The second embodiment of the present invention is described above withreference to FIGS. 10 to 13. In this embodiment, the acceptabletransmission power for the second communication service that makessecondary usage of the spectrum assigned to the first communicationservice is determined by the terminal device 400 which acts as thecoordinator of the second communication service according to theabove-described interference control model. The terminal device 400 canthereby determine the transmission power to be used for the secondcommunication service in an active manner and control the transmissionpower so as to suppress interference on the primary system 302.

Further, if the control unit 440 fails to receive radio signals from themanagement node 300 and is thus unable to acquire the latest locationdata of the primary usage node, the range of the transmission power isdetermined by counting in the margin for reducing the possibility thatcauses interference on the primary usage node. The terminal device 400can thereby start secondary usage of a spectrum autonomously and safelyeven when the terminal device 400 is located in the area where signalreceiving conditions are relatively unsuitable due to shadowing(shielding), fading or the like.

Further, with the technique of the above-described interfering marginreduction type, the margin is determined according not to the actualnumber of secondary usage nodes, but to an assumed value that isestimated inclusive of an extra number. It is thereby possible toprevent degradation of the quality of the first communication serviceeven when the number of secondary usage nodes that subscribe to thesecond communication service increases within an expected range.

<4. Application to TV Band>

FIG. 14 is an explanatory view to describe an application of theabove-mentioned first or second embodiment to TV band. In the example ofFIG. 14, a primary usage node 900 is a broadcast station of TV broadcast(TV broadcaster). Primary usage nodes 910 a to 910 c are receivingstation of TV broadcast. The primary usage node 900 provides a digitalTV broadcast service on a frequency band F1 to the primary usage nodes910 a to 910 c located inside the border 902 or 904. The inside area ofthe border 902 is a service area of the digital TV broadcast service.The shaded area between the border 902 and border 904 is a guard areawhere secondary usage of spectrum is restricted. Meanwhile, the areabetween the border 904 and border 906 is a TV white space. Secondaryusage nodes 920 a to 920 c are located in this TV white space andoperate second communication services on a frequency channel F3 which isdifferent from the frequency band F1, for example. However, even if aguard band is set between the frequency band F1 for the firstcommunication service and the frequency band F3 for the secondcommunication service, there is a risk that a fatal interference occursnot only on the secondary system but also on the primary system atposition P0, for example. Such a risk might be reduced by expanding thewidth of the guard area. However, expanding the width of the guard arealeads to a decrease of an opportunity of secondary usage of spectrum.From this point of view, to control a transmission poser of a secondcommunication service according to the above-mentioned first or secondembodiment allows for reducing interference on the primary system tofall within an acceptable range without excessively expanding the widthof the guard area.

It should be noted that a series of processing according to the firstand second embodiments described in this specification may beimplemented on either hardware or software. In the case of executing aseries or part of processing on software, a program constituting thesoftware is prestored in a recording medium such as ROM (Read OnlyMemory), read into RAM (Random Access Memory) and then executed by usinga CPU or the like.

The subject matter of each embodiment described in this specification isapplicable to various types of modes of secondary usage. For example, asdescribed above, it can be said that operation of relay node orfemto-cell to cover a spectrum hole of the first communication serviceis a mode of secondary usage of spectrum. Further, the relationshipbetween any one or more of macro-cell, RRH (Remote Radio Head), Hotzone,relay node, femto-cell and the like may form a mode of secondary usageof spectrum (such as heterogeneous network).

Although preferred embodiments of the present invention are described indetail above with reference to the drawings, the present invention isnot limited thereto. It should be understood by those skilled in the artthat various modifications, combinations, sub-combinations andalterations may occur depending on design requirements and other factorsinsofar as they are within the scope of the appended claims or theequivalents thereof.

The present application contains subject matter related to thatdisclosed in Japanese Priority Patent Application JP 2009-179366 filedin the Japan Patent Office on Jul. 31, 2009 and Japanese Priority PatentApplication JP 2010-110011 filed in the Japan Patent Office on May 12,2010, the entire contents of which are hereby incorporated by reference.

1. A method for allocating a transmission power to a secondcommunication service making secondary usage of a spectrum assigned to afirst communication service, in a node able to communicate with asecondary usage node that transmits a radio signal of the secondcommunication service, the method comprising: determining aninterference power acceptable for two or more second communicationservices when the two or more second communication services areoperated; distributing the transmission power depending on theinterference power among the two or more second communication servicesaccording to a first rule; distributing the transmission power dependingon the interference power among the two or more second communicationservices according to a second rule; selecting one of the first rule andthe second rule based on the transmission power distributed according tothe first rule and the transmission power distributed according to thesecond rule; and allocating the transmission power distributed accordingto the selected rule respectively to the two or more secondcommunication services.
 2. The method according to claim 1, wherein thefirst rule is a rule for equally distributing the transmission poweramong the two or more second communication services, and the second ruleis a rule for distributing the transmission power among the two or moresecond communication services according to a distance between eachsecondary usage node corresponding to each of the two or more secondcommunication services and a node interfered by the second communicationservice.
 3. The method according to claim 2, wherein the step ofselecting one of the first rule and the second rule includes comparing atotal capacity calculated based on the transmission power distributedaccording to the first rule with a total capacity calculated based onthe transmission power distributed according to the second rule, andselecting a rule with a larger total capacity.
 4. The method accordingto claim 3, wherein the total capacity is calculated based only on atransmission power corresponding to second communication services with ahigh priority, out of the transmission power distributed according tothe first rule or the second rule.
 5. The method according to claim 2,wherein the step of selecting one of the first rule and the second ruleincludes comparing a number of links of second communication servicesthat can be established based on the transmission powers distributedaccording to the first rule with a number of links of secondcommunication services that can be established based on the transmissionpowers distributed according to the second rule, and selecting a rulewith a larger number of links.
 6. The method according to claim 1,wherein the transmission power depending on the interference power isdetermined based on quality of a radio signal required in the firstcommunication service, an interference level or a noise level in thefirst communication service, and a path loss on a communication pathabout each secondary usage node corresponding to each of the two or moresecond communication services.
 7. A communication device comprising: acommunication unit that is able to communicate with a secondary usagenode that transmits a radio signal of a second communication servicemaking secondary usage of a spectrum assigned to a first communicationservice; and a control unit that allocates a transmission power to eachsecond communication service, wherein the control unit determines aninterference power acceptable for two or more second communicationservices when the two or more second communication services areoperated, distributes the transmission power depending on theinterference power among the two or more second communication servicesaccording to a first rule, distributes the transmission power dependingon the interference power among the two or more second communicationservices according to a second rule, selects one of the first rule andthe second rule based on the transmission power distributed according tothe first rule and the transmission power distributed according to thesecond rule, and allocates the transmission power distributed accordingto the selected rule respectively to the two or more secondcommunication services.
 8. A program causing a computer to act as acontrol unit, the computer controlling a communication device includinga communication unit that is able to communicate with a secondary usagenode that transmits a radio signal of a second communication servicemaking secondary usage of a spectrum assigned to a first communicationservice, wherein the control unit allocates a transmission power to eachof two or more second communication services and the control unitexecutes a process including: determining an interference poweracceptable for two or more second communication services when the two ormore second communication services are operated; distributing thetransmission power depending on the interference power among the two ormore second communication services according to a first rule;distributing the transmission power depending on the interference poweramong the two or more second communication services according to asecond rule; selecting one of the first rule and the second rule basedon the transmission power distributed according to the first rule andthe transmission power distributed according to the second rule; andallocating the transmission powers distributed according to the selectedrule respectively to the two or more second communication services.